A Gorn skeleton in a display case
Display cases from a Collector ship
A display case was a type of cupboard with transparent walls. It was used in exhibits to allow one to view the items kept there.
In 2256, Gabriel Lorca kept a Gorn skeleton in a display case on USS Discovery. (DIS: "Context Is for Kings")
In 2269, the Lactrans regularly brought food to the crew of the USS Ariel, always putting it near the display case, in which all captured tools and supplies brought by the crew were housed. Randi Bryce described its location being behind a house outside of the force field. Leonard McCoy then reasoned that his medical equipment was also there. (TAS: "The Eye of the Beholder")
In 2370, Odo sarcastically announced his decision to start a collection of Ferengi desiccation discs and put it in a display case in his office, with a special place reserved for Quark's remains. (DS9: "The Alternate")